Atherosclerosis has been previously investigated in the primate model by numerous investigators. Unfortunately, up until now most subjects expired during the examination. Here we present a method of vascular endoscopy that allowed us to perform serial survival observations of atherosclerosis without sacrifice of the model. Nine male and three female Japanese monkeys (Macaca fuscata) were used for the atherosclerosis models. Anastomosis of a 4mm diameter PTFE graft to the iliac, or in the case the iliac was obstructed, the abdominal aorta, under general anesthesia allowed periodic observation by balloon angioscopy. After surgery, animals were fed an atherogenic diet containing 2% cholesterol. Observations of vascular change and serum lipid analysis were performed at two-month intervals. All observations were recorded on video. Prior to commencing the atherogenic diet, we observed smooth, bluish white endoluminal surfaces, and mean total cholesterol (T-chol) was approximately 100mg/dl. After five to seven months of the high cholesterol diet, T-chol levels increased to 400-500mg/dl, atheromata were observed at the orifices of the major branches, i.e. celiac, superior mesenteric, and renal arteries, etc., and sclerosis had progressed to the aortic wall. Good data describing atherosclerotic changes in the primate were obtained without sacrifice of the model through serial in-vivo observation using vascular endoscopy. This new approach to the study of atherosclerosis in e primate model is clearly indicated for its humaneness and good data. Key words